Map Brick Procedure Texture onto Correctly Scaled Models
In Order to get the right dimension for your tile material onto the UVW map.

1 . Use UV Project From View, while in top view.
2 . If your object is a wall then you will need to use the front, left or right view.
3.  Select "Orthographic" option in the tool panel ...
4.  This will match your object you have modelled to scale.
5.  These are the brick procedure texture settings

      a. Offset 0.00  
      b. Frequency 1.0 
      c. Squash 1.0  
      d. Frequency 1.0  
      e. Scale 1.0  
      f. Mortar Size 0.002  
      g. Bias 1.0  
      h. Brick Width 0.300 (In metres)  
      i. Brick Height 0.300 (In metres)    


0.3 metres is exactly 300 millimetres.



EXTRA NOTES


  It is important to note that if you have accidentally/intentionally scale up
  or down your object in Object Mode, you will be required to apply scale before
  attempting the UV Unwrap of the model as incorrect scale will interfer with the 
  unwrap.